This invention relates to a capacity control for a variable capacity refrigerant compressor, and more particularly to a pneumatically operated capacity control valve having an integral sensor for measuring the discharge pressure of the refrigerant.
Variable capacity refrigerant compressors have been utilized in automotive air conditioning systems, with the compressor capacity being controlled by a pneumatically-operated control valve. In a typical implementation, the compressor includes one or more pistons coupled to a tiltable wobble plate or swash plate, and the control valve adjusts the pressure in a crankcase of the compressor to control the compressor capacity. In one common arrangement, for example, the compressor suction (inlet) pressure acts on a bellows to linearly position an armature in a valve passage that couples the crankcase to the compressor discharge (outlet) pressure. If the suction pressure decreases due to a reduction in the cooling load, for example, the bellows expands to open the passage, raising the crankcase pressure and decreasing the compressor capacity. When the suction pressure rises due to the decreased compressor capacity, the bellows retracts the armature to close the passage, and the compressor capacity is maintained at the reduced level. A bleed passage couples the crankcase to a suction passage so that the compressor capacity will increase if the valve passage remains closed.
Although the above-described pneumatically-operated valve can control compressor capacity in a very cost-effective manner without requiring numerous sensors for measuring various system parameters, it is still desirable to measure the compressor discharge pressure for purposes of controlling the compressor clutch and the condenser cooling fan(s). The usual approach is to mount a pressure sensor on a refrigerant line between the compressor and the expansion orifice, but variability in the position and orientation of the sensor results in variations of the sensed pressure due to transport delay and/or pooling of the refrigerant. Consistent results can only be ensured if the sensor is integrated into the compressor or control valve. Accordingly, what is needed is a pneumatically-operated capacity control valve with an integral pressure sensor for measuring the compressor discharge pressure.
The present invention is directed to an improved pneumatically-operated control valve that selectively opens and closes a passage between discharge and crankcase chambers of a variable capacity refrigerant compressor for purposes of controlling the compressor capacity, including an integral pressure sensor for measuring the compressor discharge pressure. The valve includes a plunger having an axis, a stopper biased against a seat in the passage coupling the discharge and crankcase chambers, an annular bellows and a pressure sensor. A portion of the plunger passes through the annular bellows, and one end of the bellows is attached to the plunger for axially displacing the plunger to unseat the stopper. The stopper and plunger are maintained in engagement, and have axial bores that are aligned to form a passage between the compressor discharge chamber and a cavity in which the pressure sensor is retained. In this way, stopper can be seated or unseated to close or open the passage between the compressor discharge and crankcase chambers without interrupting the passage between the discharge chamber and the cavity in which the pressure sensor is retained.